Technical Field
The present disclosure relates generally to a device for use in orthopedic surgeries, and more particularly to a plate that is attachable to the vertebrae, e.g., cervical vertebrae, and is configured and adapted to change its length to maintain constant loading of the vertebrae.
Background of Related Art
The human spinal column is a highly complex structure. It includes twenty-four discrete bones, known as vertebrae, coupled sequentially to one another to house and protect critical elements of the nervous system. The cervical portion of the spine, which comprises the neck of the spine up to the base of the skull, includes the first seven vertebrae.
For many reasons, such as aging and trauma, the intervertebral discs can begin to deteriorate and weaken. This may result in chronic pain, degenerative disc disease, or even tearing of the disc. Ultimately, the disc may deteriorate or weaken to the point of tearing and herniation, in which the inner portions of the disc protrude through the tear. A herniated disc may press against or pinch the spinal nerves, thereby causing radiating pain, numbness, and/or diminished strength or range of motion.
Many treatments are available to remedy these conditions, including surgical procedures in which one or more damaged intervertebral discs are removed and replaced with a prosthetic. However, should the prosthetic protrude from between the adjacent vertebrae and contact the surrounding nerves or tissues, the patient may experience additional discomfort. In procedures for remedying this problem, a spinal plate is affixed to the vertebrae and oriented to minimize such protrusion. In addition, the plate provides fixation and support to maintain spinal stability while the fusion occurs.
Spinal plates, and cervical plates in particular, are known in the art. Fixed cervical plates generally exhibit unalterable, static dimensions. During the natural subsidence of the spinal column after surgery, the overall length of the spinal column gradually decreases. Fixed cervical plates resist this change due to their fixed axial length, which may eventually stress the spine and cause pain or discomfort. Adjustable cervical plates attend to this predicament by providing a mechanism through which the plate is shortened to accommodate for a measure of subsidence. However, some adjustable plates require subsequent surgical procedures to adjust the axial dimensions of the plate. In addition to accommodating subsidence, it is critical for the plate to provide means to apply constant loading of the bone graft in order to promote fusion of the graft site.
A common problem associated with the use of spinal plates is the tendency of the bone screws to “back out” or pull away or otherwise withdraw from the bone into which they are mounted. This problem occurs primarily due to the normal torsion and bending motions of the body and spine. As the screws become loose and pull away or withdraw from the bone, the heads of the screws can rise above the surface of the spinal plate from one or more vertebrae.